When is the best time to observe 66 Eridani?

66 Eridani is best observed from November through January, with peak visibility during December when it transits around midnight in the Northern Hemisphere.

Where is 66 Eridani located in the sky?

66 Eridani lies in the constellation Eridanus at right ascension 05h 07m and declination -04° 39′.

What telescope do I need to follow 66 Eridani?

To follow 66 Eridani through its full brightness cycle (magnitude 5.1 to 5.6) you need any 7×50 or 10×50 binoculars — the star fades out of smaller apertures near minimum light.

66 Eridani — Variable Star in Eridanus

Observable Variable Star Excellent (65/100)

Range: 5.1 - 5.6, Period: 2.0d

Magnitude 5.1–5.6^m VariableStar Eridanus (Eri) Visible

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Observe

1Physical Properties

Magnitude 5.12

Spectral Type B9V+A1V

Star Color Blue-white (B-V -0.06)

Distance 136 ly

2Position & Identifiers

RA 05h 06m 45.7s

Dec -04° 39' 18.0"

Constellation Eridanus (Eri)

HR 1657

HIP 23794

HD 32964

SAO 131777

Flamsteed 66 Eri

Double Cat 3698

SIMBAD

3How easy to follow?

Magnitude 5.1 – 5.6 mag Amplitude 0.5 mag Period 2 d

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Equipment	Bortle 3	Bortle 4	Bortle 5
Naked eye Naked eye	Hard	V. hard+	V. hard
50 mm finder 50mm finder	Medium	Medium	Hard+
150 mm telescope 150mm scope	Medium	Medium	Medium

Easy Medium Hard Very hard Impossible

Bortle 3 = rural · 4 = outer suburbs · 5 = suburbs

4Visibility

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Best season Nov – Jan (peak: Dec)

5Survey Image

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6Comparison Stars for 66 Eri (5.1–5.6)

Nearby stable stars for estimating brightness (AAVSO)

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Size Comparison

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Compare Stars

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Spectral Classification

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Hertzsprung-Russell Diagram

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Read: The Hertzsprung-Russell Diagram — Reading Stars Like a Map

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Stellar Lifecycle

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Blackbody Spectrum

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Stellar Absorption Spectrum

Simulated absorption spectrum based on spectral type. Hover over lines to identify elements.

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Stellar Fusion

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15Stellar Notes

Variable Star

E? 5.1 - 5.6v. About 2d.

Spectroscopic Binary

B9.5, B9.5, 5.5227d, K 103.8k/s, V0 +32.6k/s, msin3i 2.38, asini 7.85. Nearly equal components; secondary is | the more massive, a mercury star. vsini of both components =<41k/s.

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